Extend commit calendar to actually show what commits were made on a date

## What does this MR do?
This MR extends the commit calendar so it acutally shows what commits were made on a date and in which project.
It is based on the optimizations @dzaporozhets made for the calendar.

## Are there points in the code the reviewer needs to double check?
The UI and how the links are generated i guess. That feels hacky at the moment :/

## Screenshot:
![commit_calendar_extend_display](https://gitlab.com/uploads/gitlab-org/gitlab-ce/5bf1631660/commit_calendar_extend_display.png)

I assume that i have to refactor this a bit more to make it a cleaner implementation, so please give me feedback on what needs to be changed :)

See merge request !326